Development of an innovative lightweight piston through process combination “casting – forging”

The development of an innovative hybrid lightweight piston for marine engines is intended to help reducing emissions and operating costs. The piston consists of a piston base and a top part. In the manufacture of the piston base, a preform is cast and the final geometry is produced by means of subsequent forming (forging). This significantly improves the mechanical properties of the component. As a result of the possible material advantages in the overall process chain, the piston base can be designed as a "lightweight component". By examining the entire "primary casting – forging" process chain, the use of materials is significantly reduced, especially in the "casting" production route, since even minor internal defects can be tolerated after the preform has been cast. For the subsequent forging process, this material pre-distribution thus represents an optimum initial forging shape. The upper part of the piston is made of a thick-film composite. Here, a nickel-alloy is applied to the piston blank by laser welding or PTA build-up welding prior to the forging process. The nickel-alloy is formed together with the base material, which in turn has a positive effect on the capacity to withstand stresses. An additional heat treatment improves the high temperature resistance. Due to the higher strength and corrosion resistance of the piston head, temperature and pressure in the combustion chamber can be increased, enabling the required reduction of emissions and fuel.